1. Field of the Invention
The present invention relates to a laminate which can be suitably used for manufacturing resin-molded circuit substrates such as MID and the like and in which a metal layer is formed on an insulating substrate molded of a resin composition.
2. Description of the Background Art
A laminate obtained by metal covering-treating an insulating substrate can be formed into resin-molded circuit substrates such as MID (Molded Interconnection Device steric molded circuit) and the like by a semi-additive method, a laser method or the like.
Upon manufacturing of such the molded articles, there have been hitherto proposed methods described in JP 2714440 and JP-B 7-24328. In these previous techniques, an insulating substrate is obtained by molding a resin composition containing a liquid crystal polyester and a powdery filler having an average particle of 0.01 to 100 μm, preferably 0.1 to 30 μm or a fibrous filler having a fiber diameter of 1 to 30 μm and a fiber length of 5 μm to 1 mm, preferably 10 to 100 μm, and metal covering-treating the surface of this insulating substrate to form a metal layer thereon.
However, in the previous techniques described in JP 2714440, a chemical bond dose not exist between a molded resin and a metal layer as described that ‘The surface of a metal is treated by any one method of sputtering, ion plating or vacuum deposition in the state where degassing of a molded article is performed in a vacuum tank while heating and at the same time the hardness of a superficial part is lowered as low as possible . . .’. For this reason, there was a problem on the adherability between a resin substrate and a metal layer, in particular, adherability after underwent the thermal load.
In addition, in the techniques described in JP-B 7-24328, the surface is subjected to the roughening treatment (etching) with a chemical solution and the irregular parts thus formed is metal covering-treated and, thus, the adherability is manifested based on the mechanical anchoring effects (anchoring effects) as described that ‘A molded article composed of a composition containing an inorganic filler in a liquid crystalline polyester is subjected to the etching treatment in advance, which is thereafter dehydrated and dried and then the surface is treated with a metal by any one method of sputtering, ion plating and vacuum deposition . . .’. Thereupon, the surface smoothness of a molded article is deteriorated and, for this reason, there was a limit on precision of the circuit pattern. In addition, there was also a problem that the strength of the superficial layer is lowered by roughening of the surface of an insulating substrate. Furthermore, there was a problem that, when the etching treatment is not performed, if the plasma treatment is not conducted, the initial adhering force is low, being not practical.
On the other hand, in order to enhance the surface smoothness, the shape is defined and fibrous and finely-divided inorganic fillers are used. However, the shape defined therein of a filler is too large to stably maintain the adherability and suppress the linear expansion coefficient lower.
For example, where a resin composition containing 70 parts by mass of a glass fiber having a fiber diameter of 11 μm and a fiber length of 3 mm relative to 100 parts by mass is molded into an insulating substrate, when a cross-section of this insulating substrate is observed, a layer having an average thickness of 13 μm composed of only a resin without a filler is formed on the superficial layer of an insulating substrate and an average distance between glass fibers in a resin is as large as 45 μm and, thus, regions relatively rich in a resin are interspersed in an insulating substrate. For this reason, the strength of the superficial layer of an insulating substrate obtained is microscopically based only on the strength of a resin. In addition, when a stress is applied to an insulating substrate, the stress concentration occurs in the vicinity of a large filler such as a glass fiber and, thus, the better adhering strength can not be obtained between an insulating substrate and a metal layer.
In addition, when a fibrous filler is used and the strength of a superficial part of a substrate is improved to suppress the thermal expansion, and when the smoothness of a substrate is maintained, if the content of a filler is small or if a fiber length of a fibrous filler is small, the reinforcing effects can not be obtained sufficiently. In particular, the linear expansion coefficient becomes large, the adherability is lowered when a molded article is expanded or constricted by the thermal load applied to the molded article in a manufacturing step of the thermal load resulting from the environmental temperature change, and a stress becomes larger applied to a packaged part such as IC and the like which is packaged to a metal layer, leading to occurrence of the erroneous operation of an article.
In addition, when a fiber length of a fibrous filler is large, the fibrous filler is broken at kneading upon preparation of a resin composition or at molding of a resin composition into an insulating substrate and, thus, the reinforcing effects can not be obtained in some cases. In addition, since the fiber density per unit volume becomes smaller, the fiber density near the superficial layer of an insulating substrate becomes smaller and, for this reason, the stress is concentrated to fibers when an insulating substrate and a metal layer are broken and, thus, the better adherability can not be obtained. In addition, when molded into an insulating substrate by injection molding or the like, fibrous fillers tend to be oriented in a flowing direction of a resin composition. Since the breaking stress is differently concentrated in this direction of oriented fibrous fillers and in a direction orthogonal to this direction, the anisotropy occurs in the adherability between an insulating substrate and a metal layer. In this case, deformation due to the warpage or the thermal load at molding is caused by manifestation of anisotropy due to the fiber orientation and, thus, the surface smoothness is deteriorated. Further, there is a problem when packaged to IC and the like.
In addition, when the fiber density of a fibrous filler per unit volume is small, the shrinkage factor is different between a part where fibers are present and a part where fibers are not present, and thus the surface smoothness of the superficial layer is difficult to obtain when molding, leading to a problem that the disadvantage occurs when wire bonding is performed at packaging of loaded parts.
In addition, when the content of a fibrous filler is too large, the filler is exposed on the surface of an insulating substrate and, in this case, when the affinity between a filler and a metal layer is lower, the adherability between an insulating substrate and a metal layer is lowered, and the scatter is produced in the adhering force distribution. In addition, even when the affinity between a filler and a metal layer is high, the interface breakage occurs between the resin phase and the filler phase at the superficial layer of an insulating substrate and, thus, the adherability between an insulating substrate and a metal layer is apparently lowered.